Early on the last day of May, one of the hugest explosions ever to shake Afghanistan resounded across the capital city, Kabul. The impact of the insurgents' tanker truck bombing, which claimed more than 150 lives and injured at least 700 others, was felt several miles away.

The explosion broke windows and cracked ceilings a mile and a half from the blast's epicenter near embassies and the presidential palace. I woke to the thunderous sound and the shaking of windows and walls. I was unhurt, and there was no lasting damage to my home, but as a journalist in Afghanistan for three years, I have found that one never gets used to violent conflict.

As strenuous as it was for me, it seemed even more so for my cat, Lola. About 20 minutes after the blast, I found her in the bathroom, cowering behind the radiator. It took almost an hour of petting and hugs to calm Lola, who was a kitten when I found her in my garden the year before.

For the next week, she seemed edgy. Small sounds startled her, and she followed me everywhere. She would caterwaul when I left the house and be clingy when I returned. She ate less and lost weight. Could Lola, I wondered, have post-traumatic stress disorder?

She certainly wasn't the first animal to be visibly shaken by Afghanistan's violent attacks. Hannah Surowinski, the director of an animal shelter in Kabul, said she frequently sees the anxiety and stress I was observing in Lola.

"Like people, animals react to trauma in many different ways," Surowinski said.

The U.S. military has seen this reaction to stress in its working dogs. Its veterinarians say about 5 percent of those that have served in Afghanistan and Iraq suffer from "canine PTSD," which makes some dogs aggressive, timid or unable to do their jobs.

The diagnosis, known as C-PTSD, is still debated. But research is growing, said Stacy Lopresti-Goodman, an associate professor of psychology at Marymount University in Arlington, Va. She has studied the topic for much of the past decade, and says similarities in brain structures responsible for stress response could cause animals to respond to trauma the way people do.

Lopresti-Goodman researched hundreds of chimpanzees used in biomedical research, about one-quarter of which displayed symptoms of PTSD for years after their retirement. Scholars have also documented PTSD symptoms in parrots that were captured in the wild, kept as pets then abandoned.

Others have detected such symptoms in African elephants. One 2013 study focused on complex, kin-based groups of elephants in two national parks in Kenya and South Africa that witnessed disruptive events such as mass culling, poaching, translocation or capture. Some, the researchers wrote, displayed behaviors similar to PTSD in humans. Lopresti-Goodman said they are observable reactions to events and objects that might remind the animal of the traumatizing event.

Some animals might pace, weave their heads back and forth or bite themselves, she said. Other signs are self-calming techniques, such as excessive licking, rocking or hiding. So is what any pet owner might call depression — loss of interest in socializing, eating or playing.

Lopresti-Goodman recalled a chimpanzee named Poco, who lived at a chimp sanctuary in Kenya, where she studied symptoms of PTSD in orphans of the bushmeat trade. Many sanctuary's residents, like Poco, were captured as infants and sold as pets after witnessing their families being slaughtered for meat.

Poco was kept in a tiny cage suspended from a ceiling for years, Lopresti-Goodman said. Decades after his rescue and relocation in 1995, Lopresti-Goodman said, he remains "easily startled, always on guard, often socially withdrawn, clasps himself and rocks, and can often be found poking himself with sharp thorns."

Even after successfully integrating into a large social group in semi-natural habitat, some of the chimps still carried emotional scars from trauma.

The good news is that animal stress and anxiety disorders can be treated. Prescription medications, such as antidepressants or anti-anxiety drugs, are available for animals. But Lopresti-Goodman prefers "re-establishing safe environments and trusting relationships."

Surowinski agreed. "It helps if the animal is in a familiar territory with familiar faces," she said, recalling one bombing that sent the animals into a frenzy. "The fact that they were in familiar territory with their own kennel that they could take shelter in was almost certainly a benefit."

Lola, for her part, is doing better. My housemate and I no longer leave her alone for very long, and we give her plenty of attention. Weeks later, she still jumps at sounds as slight as the dropping of a spoon — and, of course, at the sound of gunfire. She no longer cries when we leave, but she won't place a paw outside the front door — an impulse my previous cats couldn't resist.

She's also developed a habit of licking my hand after I pet her. I believe that's Lola's way of soothing herself, so I let her do it.